1. Field of the Invention
This invention relates to an apparatus for drying powdered or granular materials (called hereunder materials) such as plastic materials, processed food materials, chemical materials for medical use, etc. by causing them to be subjected to dielectric heating by means of microwave (the drying operation including crystallizing the materials in the case of the materials as non crystallized polyethylene terephthalate, etc.).
2. Prior Art
This kind of apparatus for drying the powdered or granular materials has been hitherto proposed as shown in Japanese Unexamined Patent Application No. 301310/1989. The conventional drying apparatus for the materials comprises a transversely extending drying tank having a material inlet and outlet at one end and the other end of the tank in its longitudinal direction, and a microwave application unit for applying microwaves to the material of plastic material fed into the drying tank, wherein the drying tank has therein a rotary shaft mounting a plurality of disk-like shaped partitions to define partition spaces between adjacent partitions, the partitions being provided with agitating blades for agitating the material placed in the partition spaces and sending the materials to one of the partition spaces adjacent to the material outlet, and an exhaust port for the material at the side of the material outlet being provided with a rotary feeder.
The conventional drying apparatus causes the material placed in each partition space to be orderly transmitted to the partition space adjacent to the material outlet by turning the agitating blades, so that there may cause no dispersion of residence time of the material in the drying room, thereby enabling the material as a whole to be dried uniformly and continuously. However, the conventional art does not include a feature for providing the inside of the drying room with various distribution of temperatures, so that the material is not dried at separate drying temperatures. In other words, in case that there are different distribution of heating temperatures at the specific locations in the drying room, such as at the inlet, the central part of the room or the outlet, temperature control by the conventional apparatus is unstable and poor in accuracy since the apparatus controls temperatures by regarding only a heating temperature detected at a specific detection point as that of the whole drying room.
Also, the partitions, the partition spaces and agitating blades of the conventional example are provided transversely at the lower part of the drying room, so that there is such a defect that any materials of lower specific gravity supplied from the material inlet are likely to shortly pass over the upper parts of the agitating components.
Furthermore, the material outlet of the conventional example is so constituted that the powered or granular materials to be dried fall out of the outlet by their weights and the materials cannot be agitated by the agitating blades. Hence, there are such problems that the material outlet part provides a dead space where the materials are not agitated and happen to be solidified by microwaves.
Additionally, provision of the rotary feeder at the exhaust port at the side of material outlet makes hard a stable keeping of level of the materials in the drying tank, leading to hardness of a constant quantity control.
The present invention has been designed to overcome all of the above problems.